Which statement correctly defines the half-life of a radioactive isotope?
Half of the time taken for the activity of the isotope to fall to zero
The time taken for all the radioactive nuclei in a sample to decay
The time taken for the activity of the isotope to decrease to half of its initial value
Half of the time taken for the number of radioactive nuclei to halve
144 exam-style questions on CIE IGCSE Physics 5.2.4a Half-life. Each one has a worked solution and a mark scheme showing where the marks go.